Vivariums house a number of animals, typically test animals, such as mice, in a number of cages, often a large number. The test animals are frequently used to test drugs, genetics, animal strains, husbandry experiments, methods of treatment, procedures, diagnostics, and the like. We refer to all such uses of a vivarium as a study.
Use of altering the temperature of an animal in a vivarium for husbandry or study purposes is well established. See, for example, Temperature Regulation in Laboratory Rodents, by Christopher J. Gordon, Cambridge University Press, 1993. In particular, refer to chapter 4, “Thermoregulatory effector responses.” Although many animals will seek a warmer or cooler location as a means of regulating their body temperature, many rodents, mice in particular, alter their behavior as a way to regulate their body temperature. As Mr. Gordon says, (ibid, p. 99), “The behavior sensing of temperature is exquisitely sensitive, and behavior effectors for modulation of the ambient thermal environment can be shown to operate continuously.” Therefore, using heat as a reward for desired behavior, either natural behavior or learned behavior, is an effective way of both changing and measuring animal behavior. Animal behavior is one crucial aspect of many animal studies.
The warmth or body temperature of an animal is typically either the skin temperature or the internal body temperature. There are various ways to measure these temperatures, both directly and indirectly. Body temperature can often be computed from known models using environmental measurements and can also be estimated by observing behavior.
Prior art typically altered the temperature of an animal by changing the temperature of its environment. This was typically done by altering the air temperature, either by controlling the ambient temperature of the vivarium, by heating the cage, or by providing controlled temperature air into the cage. Gordon refers to all of these as, “the ambient thermal environment.” An alternative method was to provide conducted heat such as a warmed cage floor, nesting area, or heating pad.
A weakness of prior art methods was that the cage temperature was kept cooler than the animals preferred living temperature, except when providing the heat reward. This is considered inhumane animal conditions.
Yet another weakness of prior art methods is to move the animals from their primary cage to an experimental cage that is equipped to provide the heat reward. Many animals require an acclimatization period after being transferred to another cage, often measured in days, during which any data collected represents unnatural behavior and thus of little scientific value. Results are further skewed by pheromones and other contaminants of the reused destination cage. The experimental cage may require light for a human experimenter or automated system to detect the behavior to be rewarded. Both the movement and light may be undesirable by the animal and may impact the study results.
Yet another weakness of these prior art methods of providing warmth to an animal is that generally all animals in the cage are heated equally, and thus rewarded equally. Although a cage might be heated non-uniformly, no method of reliably heating only a single, selected animal in a cage of multiple animals exists in the prior art. Therefore, it has not previously been possible to reward specific behavior that required multiple cohabitating animals. Examples include social behaviors such as grooming, mating, sharing, leading, teaching, parenting and fighting.